Telephone-transmitter.



C. L. CHTSHOLM.

TELEPHONE TRANSMITTER. APPLICATION FILED MAVSl, ma.

Patented June 13, 1916.

ATTORN EY CHARLES L. CHIS HOLM, OF LONDON,ONTARIO, CANADA.

TELEPHONE-TRANSMITTER.

Specification of Letters Patent.

Application filed May 31, 1913. Serial No. 771,110.

To all whom it may concern:

Be it known that 1, CHARLES L. Criisr o avi, a subject of the King of England, res d ng at London, Province of Ontario, Dominion of Canada, have invented a new and useful Telephone-Transmitter, of which the following is a specification.

This invention has reference to improvements in telephone ject is to provid a transmitter of increased power and fullness of tone and of greater sensitiveness thai heretofore, and also to produce a transm of packing is pra vtically eliminated, and, moreover, wherein a greater amount of resistance material may be employed than heretofore without danger of packing or damping the diaphragm.

In accordance sound waves directly impinge, forms one wall of the granule chamber, while within the granule chamber there is a back contact speech receiving diaphragm. toward the back contact and in cross section the marginal wall of the granule chamber deflnesa compound curve, whereby there are neither shoulders nor angles presented to the granules lodged within the chamber and the granules therefore, whilethe instrument is in operation, are ina state of great .mobilv ity, so that the vibrations of the.diaphragm cause such agitation of the granules that even should the granules become packed,

"as might occur while the instrument was quiescent, the first impulse of the diaphragm will depack the granules and subsequent vibrations maintain the" depacked condition.

Practice, however, demonstrates that even the suggested possibility of packing while the instrument is quiescent is not experienced, and this is especially true when those I the granules come in the curved marginal surfaces with whic contact, and notably walls of the granule chamber and the inner face of the diaphragm, are highly polished.

transmitters, and its obter wherein the liabilitywith the present invention. the diaphragm upon which speech or other,

The invention will be best understood from a consideration tailed description, taken in connection with the accompanying drawings forminga part of this specification, with the further understanding that while. the drawings show a practical form of the invention, the latter is not confined to any strict conformity with the showing of the drawings, but may be changed and modified so long as such changes and modifications mark no material departure invention.

from the salient features of the In the drawings :Figure 1 is a cross section of a transmitter embodying the present invention and showing so much thereof as is necessary to illustrate the invention, the view being drawn on a somewhat enlarged scale.

Fig. 2 is a section similar to Fig. 1 but drawn to a greatly enlarged scale and showing a little more than half the transmitter. Fig. 3 is a detail section of a portion of the structureshown in Fig. 2 but drawn to a still larger scale, and indicating some features in addition to the showing of Fig. 2.

, Referring to the drawings, there is shown a ring 1 having an axially directed flange E2 internally threaded, as indicated at 3, while the ring and flange are externally threaded as indicated at 4. The ring is relatively Patented June 13,1916.

of the following de- I broad diametrically, and is provided with i a central passage 5 for a purpose which will hereinafter appear. Lodged on the ring lQis a diaphragm 6 preferably of mica, and this diaphragm is held to-the ring by another ring 7 exteriorly threaded to threads 3, so that when the ring 7 is screwed into the flange 2 it will bear upon the mica diaphragm and clamp it in place. One end of the ring 7 is substantially as wide astlie portion of the rin phragin 6 rests, ring 7 terminates in a flange 8 which may extend radially beyond the threaded outer edge of the ring 7.

ring 7 is formed with an ferential rabbet 9 forming a seat for the edge portion of a diaphragm 10, this seat being of very small diametric extent, so that the diaphragm has the smallest practicable peripheral support. The diaphragm is lodged upon the seat formed by the rabbet 9 and is cemented or otherwise firmly secured in the rabbet, care being taken to avoid undue strain.

The flanged end 8 of the internal circum fit the screw The internal diameter of the ring 7 at its thickest portion, which is at the-end remote from the diaphragm 10, is considerably less than the internal diameter of the ring where the rabbet 9 is formed, and the-inner wall of the ring between the two ends of different diameters is concave, as indicated at 11, from the rabbet' 9 toward the other end of the ring for a distance and then is convex, as indicated at 12 as it approaches the thicker end of the ring, so that the inner Wall of the ring is in the form of a compound curve. The ring 7, together with the diaphragms 6 and 10, forms a granule chamber in which is lodged a quantity of granules 13, usually of carbon, but such granules may be replaced by any other suitable resistance medium, for the present invention is not necessarily limited to the use of carbon ranules.

Within the granule chamber and at an appropriate distance from the diaphragm 10 is a back contact 14 there made of carbon and secured to a support 15 from the center of which there projects a stem 16 extending through the diaphragm 6 at the center of the latter, and at the center of the opening 5 through the ring 1. Applied to that face of the diaphragm 6 remote from the support 15 is a block 17 which may be of metal, since it is the purpose of this block to provide an appropiate weight. The stem 16 extends through the block 17 and is threaded at its free end for the reception of a nut 18 serving to hold the block 17 in firm contact with the diaphragm 6, so that the diaphragm is rigidly clamped between the support 15 and theblock 17. The nut 18 also serves as a clamp nut for one terminal 19 of a conductor 20 the other terminal 21 of which may be clamped by a screw 22 to a block 23 of insulating material carried by the rin 1 atfo'ne side of the opening 5. The block 1 is preferably of the same diameter as the packing or support 15 for the back contact 14, so that the diaphragm 6 is clamped between these blocks at equal distances from the center throughout the circumference of the block 17 and support 15, these members being round or cylindrical. Moreover, care is taken that the stem 16, support 15, and block 17 are in concentric relation to the ring 1, for it appears from actual practice that eccentricity of the parts is liable to interfere with the best results.

Applied to the exteriorly threaded portion of the ring 1 with its flange 2 is a cap member 24 anda back member 25, together constituting an inclosing casing for the microphonicelement ofthe transmitter. The cap member 24 is so related to the diaphragm as to provide a sound chamber 26 and the cap member also has a centrally located and axially extended boss 27 provided with anaxial passage 28 leading to the chamber 26. The boss 27 is exteriorly threaded for the reception of a mouth piece which may be similar to mouth pieces as usually provided with telephone transmitters, except that the design of this mouth piece is adapted to the transmitter of the present invention, which, as will hereinafter appear, is minute as compared with the ordinary commercial transmitters.

The rear member 25 of the casing is arranged to inclose the rear portion of the microphonic element, thereby protecting it from injury, and it may also have a centrally disposed stem 29, by means of which the entire instrument can be suitably mountof a desk set or the arm of a Wall set.

The marginal portions of the back contact 14 may be advantageously beveled, as shown in Fig. 3, or rounded as shown in Fig. 2 so that the front face of the back contact, which face should be polished, is somewhat less extensive than the support 15, and it is advantageous to cover the exposed marginal edge of the support 15 for the back contact and in some instances the marginal edge 30 of the back contact, with insulating material indicated at 31 in Fig. 3, while the corresponding portion of the inner wall of the ring 7 may have a coating 32 of insulating material, as also indicated in Fig. 3. Under some circumstances either coating of insulating material may be employed and the other omitted, and under some circumstances both coatings may be employed, while the extent of the coating 32 on the inner wall of the ring 7 may be varied in accordance with circumstances.

It has been hereinbefore stated that the instrument of the present invention is comparatively minute. In order to give some idea of the size of the instrument it may be stated that in a commercial form of the instrument giving excellent results, the diaphragm 10 is about fiveone-thousandths of an inch thick and about twenty-five thirtyseconds of an inch in diameter. The back contact 14 is a one-halfinch standard back contact with rounded or beveled edge, the rounded or beveled edge being peculiar to the present invention, and not present in the standard back contacts of commerce. The

- diaphragm 6, which may be termed the back six grains has given good results, wherefore such weight 17, as compared with the. parts with which it is associated, may be described as relatively heavy. The depth of the granule chamber is about four thirty-seconds of an inch, while the distance between the inner face of the main or speaking diaphragm 10 and the corresponding face of the back contact 14 is about two thirty-seconds of an inch. The free portion of the back diaphragm 6 between inner walls of the rings 1 and 7 is about three sixty-fourths of an inch. These various measurements are those of a transmitter giving most excellent results and indicate the minute size of the instrument, it being understood that the diaphragm 10 is the speaking diaphragm,

that is, the diaphragm against which speech or other sounds are directly uttered, and nothing is interposed between the speech receiving diaphragm and the granules which bear directly againstthe inner face of the diaphragm throughout the greater portion of the free area of the inner face as defined by the extremely narrow seat formed by the rabbet 9.

It is found advantageous to polish the inner face of the diaphragm 10 and the inner walls of the ring 7 and other metal parts within the granule chamber, as well as the exposed face of the back contact 14, and in order to maintain the polished condition it is advantageous to plate the metal surfaces presented within the granule chamber with some nontarnishable metal, such as gold, but this plating, because of the minute size of the whole structure, is not at all prohibitive, so far as cost is concerned, since the entire instrument may be produced at but a small fraction of the cost of any of the commercial types of transmitters to be found upon the market. In the commercial form the metal parts of the transmitter may be of brass or some other suitable metal with the exposed surfaces nickle plated, and the surfaces within the granule chamber plated with gold or platinum or some other nontarnishable metal.

The front or voice receiving diaphragm 10 is preferably so made as to have a high fundamental, so that its natural rate of vibration exceeds the rate. of vibration of the normal human voice. The diaphragm 6 has a certain degree of flexibility and a different natural rate of vibration from the diaphragm 10, but this rate of vibration is modified by the presence of the weight 17 located outside of the granule chamber. The addition of the weight 17 is found to very markedly increase the sensitiveness of the instrument over the identical instrument with the Weight omitted, and by making this weight greater or smaller within limits the sensitiveness may be correspondingly varied so that the instrument is readily adapted to persons who are partially deaf. This last characteristic is of value to persons so afflicted since deaf persons usually speak with but little force of voice and a transmitter of greater sensitiveness than ordinary transmitters is then of advantage. Moreover, the extremely minute size of the commercial form of the instrument adapts it particularly for use as an individual transmitter, that is, one which may be carried about by the owner to be attached to or removed from the telephone line at local stations may be desired, and the extreme small size of the instrument renders its presence upon the person of the user unobtrusive, for it may be housed together with a collapsible mouthpiece in a receptacle of the size, shape and characteristics of a medium size watch case. Moreover, the minute size of the transmitter permits its employ" ment on desk sets which may be so light without any sacrifice of stability that the entire weight of the desk set may be less than twice the weight of an ordinary telephone receiver, which latter may be used in connection with adesk set and constitute the stabilizing element therefor.

Greattrouble has been experienced heretofore with telephone transmitters because of the packing of the granules in the granule chamber and this packing has been avoided by mechanical devices, whereby the granules may be jarred from time to time, and in the great majority of commercial telephone outfits it is not at all unusual to have very poor service due to persistent packing of the granules which can only be remedied by jarring the transmitter although such treatment of the transmitter is liable to injure its adjustments.

lVith the present invention packing appears to be wholly eliminated, and this result appears to be due to the presence of the curved wall 12 in conjunction with the curved wall 11 forming the granule chamber, so that there is no point where the granules may lodge and. therefore, pack. The polishing of the walls 11 and 12, as well as the inner face of the diaphragm 10 also contributes to this desirable result, but packing is still present in instruments identical with the showing of the drawings except that the wall 12 is a cylindrical wall instead of a wall in constantly expanding relation as it retreats from the diaphragm 6.

\Vhile not being committed to any particular theory of action, it is assumed. that the curved surface 12 presents no point of lodgment for any of vigorous action of the diaphragm 10 in response to the impact of sound waves so agitates the granules that they slip and slide over the smooth rounded surfaces without the possibility of finding anchorage, and so permitting the piling up of other granules until there occurs between opposite sides of the circuit in the granule chamber a mass of closely packed granules in bridging relation to the metallic parts permitting so great a flow of current as to smother out the variathe granules, while the tions of current produced in other parts of the granule chamber.

Experience has proven that the present invention makes it possible to add much more resistance material to the granule chamber without either danger of packing or of damping the diaphragm against which sound is uttered. Because of this it is found that the transmitter is capable of carrying a heavier current than commercial types of transmitters, and that a greater variation of resistance is obtainable and this variation of resistance very closely approaches the ideal conditions, so that speech is transformed into electric undulations corresponding so closely to sound waves produced by the human voice that the naturalness or timber of the human voice is preserved and articulation is particularly distinct, wherefore the listener has no difliculty in understanding speech or in recognizing the speaker from the voice. These advantageous conditions are found to be due to the presence of the weight 17, and the curved Wall 12, as well as the back contact, the speech receiving diaphragm 10 forming the front wall of the granule chamber, and the polished walls of the granule chamber, although the addition of either the weight 17 or the curved surface 12 is found in actual experience to add to the performance of the transmitter and the absence of either is found to have a noticeable detrimental effect. All the features enumerated appear to be contributed to the final result obtained which is very noticeably superior to the results obtained by the best commercial transmitters, and while a transmitter following the construction herein described, but omitting the curved wall 12 and weight 17 is in itself superior in performance to the ordinary commercial telephone transmitter, it is found in practice either over long lines under actual commercial conditions, or in the laboratory over artificial lines of great extent, the sensitiveness of the transmitter including the weight 17 and curved wall 12 is very noticeably improved, while the heretofore unavoidable packing of the granules is wholly eliminated, wherefore the best results of which the instrument is capable are always obtainable under ordinary working conditions, and without the necessity of depacking devices. If there be any tendency at all to pack, this is avoided when the instrument is in action by the automatic depacking tendency of the diaphragm against which speech is uttered, and which forms the front wall of the granule chamber.

The great sensitiveness of the instrument due to the presence of the weight 17 and ti elimination of packing due to the presence of the curved wall 12 in conjunction with the reverse curved Wall 11, permits the employment of a greater mass of granules than is possible with some of the best types of commercial transmitters. Heavier current may, therefore, be employed without either danger of unduly heating or burning the microphonic element, or of producing the condition known as frying, wherefore the power of the transmitter of the present invention may be greatly increased over and above that of commercial types of transmitters without any danger to the instrument or in any manner interfering with its action.

The efliciency of the transmitter may be more 01' less reduced by leakage between the marginal portions of the back contact and the curved surface 12, especially Where the back contact is a little eccentric to the surface 12, thus producing paths of lower resistance at some points than at others. The insulating material 31 or 32 or in some instances both, avoids such a condition by creating a longer path for the current through the granules between the back contact and the side walls of the granule chamber than between the back contact and the diaphragm 10, wherefore such a detrimental condition as mentioned cannot arise. The presence of the insulation 31 or 32 or both is not absolutely essential but under some conditions will be found advantageous.

\Vhat is claimed is:-

1. A telephone transmitter provided with a. granule chamber having a diaphragm forming one wall thereof and designed to receive the direct impact of sound waves, said granule chamber inclosing a back contact and having the marginal Walls reversely curved from the back contact toward the sound receiving diaphragm, the tw curves being substantially equal.

2. A telephone transmitter provided with a granule chamber having a diaphragm forming one wall thereof and designed to receive the direct impact of sound waves, said granule chamber inclosing a back contact and having the marginal walls reversely curved from the back contact toward the sound receiving diaphragm, said reversely curved walls being concave adjacent to the sound receiving diaphragm and convex adjacent to the back contact. the concave and convex portions being substantially equal in extent of curvature.

3. A telephone transmitter provided With a diaphragm for receiving the direct impact of sound waves, a granule chamber of which the diaphragm forms the front wall, another diaphragm, and a back contact mounted thereon and constituting the rear wall of the granule chamber with the back diaphragm forming a yielding support for the back contact, and a relatively heavy weight attached to the back diaphragm exterior to the granule chamber and movable with said diaphragm.

4. A telephone transmitter provided with adiaphragm for receiving the direct impact of sound waves, a granule chamber of which the diaphragm forms the front wall, another diaphragm, and a back contact mounted thereon and constituting the rear wall of the granule chamber with the back diaphragm forming a yielding support for the back contact, and a weight attached to the back diaphragm exterior to the granule chamber and movable with said diaphragm, the granule chamber having marginal walls extending from the sound receiving d1aphragm to the back diaphragm and decreasing in diameter in said direction, said walls being reversely curved to like extents with a concave portion adjacent to the sound receiving diaphragm and a convex portion adjacent to the back diaphragm.

5. A telephone transmitter, a back contact expanding at the margins from the front face toward the rear face, and a granule chamber inclosing the back contact and having a diaphragm arranged for the direct reception of sound waves constituting the front wall of the granule chamber, and the marginal walls of the granule chamber expanding from the rear toward the front in a reverse curve, convex adjacent to the back contact and concave adjacent to the sound receiving diaphragm, the curvatures being of substantially equal extents.

6. A telephone transmitter, a back contact expanding at the margins from the front face toward the rear face, and a granule chamber inclosing the back contact and having a diaphragm arranged for the direct reception of sound waves constituting the front wall of the granule chamber, and the marginal walls of the granule chamber expanding from the rear toward the front in a reverse curve, convex adjacent to the back contact and concave adjacent to the sound receiving diaphragm with the curvatures of substantially equal extent, said granule chamber having its rear wall in the form of adiaphragm carrying the back contact and provided with a weight exterior to the granule chamber and participating in the movements of the back diaphragm.

7. A telephone transmitter having a granule chamber with walls of conducting material with a diaphragm also of conduct ing material arranged for the direct reception of sound and constituting the front wall of the granule chamber in electrical contact with the body thereof, a back contact within the granule chamber in operative relation to the diaphragm, a rear diaphragm of insulating material carrying the back contact and insulating it from the walls of the granule chamber, and insulating material interposed between the margins of the back contact "1d the corresponding portions of the side w alls of the granule chamber, the extent of insulation beingthat of the projection of the back contact into the granule chamber.

8. In a telephone transmitter, a granule chamber provided with a sound receiving diaphragm constituting its front wall, an insulating diaphragm constituting its rear wall and with side walls expanding from the rear diaphragm toward the front diaphragm, a back contact carried by the rear diaphragm wholly within the granule chamber, and a coating of insulation separating the adjacent portions of the margin of the rear contact from the side walls of the granule chamber.

9. In a telephone transmitter, a granule chamber provided with a sound receiving diaphragm constituting its front wall, an insulating diaphragm constituting its rear wall and with side walls expanding from the rear diaphragm toward the front dia phragm, a back contact carried by the rear diaphragm wholly within the granule chamber, and a coating of insulation separating the adjacent portions of the margin of the rear contact where within the granule chamber from the side walls of the granule chamber, said coating being produced upon both the marginal walls of the back contact and the side walls of the granule chamber.

10. A telephone transmitter provided with a chamber containing resistance material and having a back contact and a supporting diaphragm therefor, the chamber increasing progressively in diameter as it recedes from said diaphragm, with the inner marginal wall convex adjacent to the supporting diaphragm for the back contact for a distance from said diaphragm substantially that of the projection of the back contact into the chamber containing resistance material.

11. A telephone transmitter provided with a chamber containing resistance material and having a back contact within the chamber, a supporting diaphragm for the back contact constituting the rear wall of the chamber, and a relatively heavy weight on the back diaphragm exterior to the chamber and freely movable with said diaphragm, the chamber convexly increasing in. diameter as it recedes from the diaphragm for a distance substantially that of the projection of the back contact into said chamber.

12. A telephone transmitter provided with a chamber containing resistance material and having a back contact within the chamber, a supporting diaphragm for the back contact constituting the rear wall of the chamber, and a weight on the back diaphragm exterior to the chamber and freely movable with said diaphragm, the chamber increasing progressively in diameter as it recedes from the diaphragm, and the inner marginal wall of the chamber being convex adjacent to the said diaphragm for a distance away therefrom corresponding to the projection of the back contact into the chamber containing resistance material.

13. A telephone transmitter provided With a chamber containing resistance material, a diaphragm forming the front wall of the chamber, another diaphragm forming the rear Wall of the chamber and more yielding than the front diaphragm, a back contact mounted on the rear diaphragm and lodged within the chamber, and a relatively heavy Weight fast to the back diaphragm exterior to the chamber and freely movable with the diaphragm.

1*. A telephone transmitter provided with a chamber containing resistance material, a diaphragm forming the front Wall of the chamber, another diaphragm forming the copiel of this patent may be obtained for five cents each, by addressing the rear Wall of the chamber and more yielding than the front diaphragm, a back contact mounted on the rear diaphragm and lodged within the chamber, and a relatively heavy Weight fast to the back diaphragm exterior to the chamber and freely movable With the diaphragm, the chamber convexly increasing in diameter as it recedes from the rear diaphragm for a distance substantially that of the projection of the back contact into said chamber.

In testimony that I claim the foregoing as my own, I have hereto aflixed my signature in the presence of two Witnesses.

CHAS. L. CHISHOLM. \Vitnesses JOHN H. Smcnns, EDITH L. BROWN.

Commissioner of Petentl,

Washington, D. 0." 

